A variety of methods are known in the food preparation art for preparing snack foods such as potato chips and other forms of vegetable and grain chips such as corn or tortilla chips. Most of these methods, however, rely on cooking techniques in which the potato or other chip is immersed in a reservoir of hot oil for a period of time. Known as "deep fat" frying, the effect of this cooking process is to substantially reduce the water content of the potato slice while allowing some fat uptake from the hot oil reservoir. The moisture content of fresh potato slices is typically about 85% of the weight of the slice while "deep fat" fried potato chips commonly have a moisture content of less than 5% by weight. The deep fat frying process, however, also typically results in a finished potato chip having a fat content from about 30% to about 45% of the total weight of the finished chip.
The high fat content of conventionally prepared potato chips is considered undesirable by many people because of the increased caloric value and the relatively short shelf life of the resulting chip. The fat stored in a potato chip can become rancid after long term storage, imparting an undesirable odor and taste to the chip. A number of cooking methods have been developed in the past to reduce the fat content of potato chips and the like. U.S. Pat. No. 3,365,301 to Lipoma et al., for example, discloses a process for making fried chips by partially cooking potato slices in an oil bath at higher temperatures and for shorter periods of time than normally used in conventional oil immersion cooking processes, with a final cooking step employing electromagnetic heating, such as microwave heating. The higher temperature and shorter time period of the oil immersion portion of the Lipoma cooking process is believed to result in a final chip having a reduced fat content. This approach, however, does not eliminate the uptake of fat by the chip during the first step of the cooking process. Another approach, disclosed in U.S. Pat. No. 4,283,425 to Yuan et al., is to prepare potato chips by coating a raw potato slice with globular proteins and an optional layer of edible oil on top of the protein coating. The potato slice prepared in this fashion is then cooked by microwave heating. While eliminating the step of deep fat frying, the Yuan approach still produces a potato chip having an exterior coating of at least globular proteins. At column 3, lines 47-59, the Yuan patent states the protein coating is an essential element in successfully microwaving the potato slices. Use of microwave heating alone to prepare potato chips has previously been considered unsuitable because of gelatinization, a tendency of starches in the potato slice to coat the exterior surfaces of the slice and to form a gummy seal which hardens with further heating. The Yuan patent, for example, notes at column 2, lines 45-50 that efforts to remove more than 3% of the moisture content of a potato slice by microwave heating causes starch gelatinization.
The present invention further relates to the use of a unique meander waveguide structure in conjunction with a novel conveyor belt. Various sorts of microwave waveguides are known as shown in, for example, U.S. Pat. No. 3,469,996 to Endres and U.S. Pat. No. 3,765,425 to Stungis et al. The Endres patent shows a zig-zag waveguide configured to direct microwave energy downward through slots in a lower planar surface of the waveguide onto a conveyor belt passing below the waveguide in order to temper shortening carried on the conveyor belt. The Stungis patent discloses a serpentine waveguide repetitively engaging a conveyor belt, in order to expand tobacco stems and lamina.
The use of conveyor belts to convey raw and partially prepared food products is also known. In the field of conveyor belts, U.S. Pat. Nos. 3,870,141 and 4,556,142 to Lapeyre, for example, show conveyor belts having links in the form of flat lattice type structures. U.S. Pat. No. 4,993,543, to Lapeyre, discloses a type of conveyor belt link having a protruding drive tooth. The drive teeth of the links engage a drive sprocket that powers the conveyor belt. These conveyor belt structures, however, possess only a flat conveying surface. Limp, raw food products conveyed by these belt structures would normally result in finished food products having a similarly flat shape.
Thus there still exists a need for an apparatus and method of preparing potato and like vegetable chips, as well as corn, tortilla and other grain chips, having all of the taste, consistency and shape of the widely known and broadly appreciated deep fat fried potato, corn and tortilla chips, but which are fat free or virtually fat free and which are curved.